#include <stdio.h>

int main() {
    int n, i, j, tmp;
    float sum = 0.0;
    scanf("%d", &n);
    for (i = 1; i <= n; i++) {
        tmp = 0;
        for (j = 1; j <= i; j++) {
            tmp += j;
        }
        sum += 1.0/tmp;
    }
    printf("s=%f\n", sum);
    return 0;
}
